Aquatic-adapted plants, which bloom in water or are sometimes stranded on land, have been called var. stipulacea (although that epithet may not be the oldest one available for the taxon). They produce ovoid-conic to short-cylindric inflorescences 10-40(-60) mm, prostrate aerial stems, and leaf blades that are glabrous with acute to rounded apices. Terrestrial forms of this ecotype usually are spreading-pubescent and often bear ocreae that are foliaceous, green, and flared distally, characters found only in North American plants (R. S. Mitchell 1968).

Terrestrial-adapted plants, referred to var. emersa, bloom on moist soil and produce short- to elongate-cylindric inflorescences 40-110(-150) mm, spreading or erect aerial stems, and leaf blades that are appressed-pubescent with acute to acuminate apices. They produce ocreae that are entirely chartaceous and not flared distally. Emergent and terrestrial plants of this ecotype exhibit less phenotypic plasticity and a lower frequency of heterostyly than do plants of the aquatic ecotype (R. S. Mitchell 1968).

R. S. Mitchell and J. K. Dean (1978) and H. R. Hinds (2000) recognized var. amphibia, the Eurasian element, as introduced in New York and New Brunswick, respectively. These plants are morphologically intermediate between the North American ecotypes and often indistinguishable from North American plants (Mitchell and Dean).

The Meskwaki and Ojibwa used leaves, stems, and roots as a drug to treat a variety of maladies, the Potawatomi used roots to treat unspecified ailments, and the Lakota and Sioux used plants for food (D. E. Moerman 1998).

From Flora of Indiana (1940) by Charles C. Deam

[Deam delineates two species in this complex: P. amphibia sensu stricto has glabrous peduncles and are aquatic plants with floating leaves bearing obtuse or subacute apices. His second species, P. coccinea, has pubescent/glandular peduncles, a semi-aquatic to terrestrial habit, and very acute to acuminate leaf apices. Regarding P. amphibia s.s. Deam observes the following:] All of our reports for Persicaria amphibia (L.) S. F. Gray, Persicaria fluitans (Eaton) Greene, Polygonum amphibium L., and Polygonum amphibium var. aquaticum Willd. I am referring to this species. The nomenclature of this and the next species [Polygonum coccineum] has long been so involved that their distribution in the state can not be determined from the published records. It is, no doubt, restricted to the lake area of the state.

[Regarding P. coccinea Deam observes that] this species is an aggregate to which, since I am not able to separate it satisfactorily into forms and varieties, I am referring all reports from Indiana of the following: Persicaria coccinea (Muhl.) Greene, Persicaria coccinea var. asprella Greene, Persicaria coccinea var. tanaophylla Nieuwl., Persicaria emersa (Michx.) Small, Persicaria grandifolia Greene, Persicaria lonchophylla Greene, Persicaria mesochora var. arenicola Nieuwl., Persicaria Muhlenbergii (Wats.) Small, Persicaria pratincola Greene, Persicaria tanaophylla Nieuwl., Polygonum coccineum var. pratincola (Greene) Stanford, Polygonum emersum (Michx.) Britt., Persicaria mesochora Greene, and Polygonum Muhlenbergii (Meisn.) Wats. The named variations of this species and the segregates from it are based mostly upon leaf characters, such as the general shape and base of the blades. Using these characters, I have one specimen which belongs to three species. I have a series of specimens of this species all from the same rootstock which might be referred to different species. The species is perennial. One year it may be in deep water, the next year it may be in shallow water or for part of the year it may be on dry ground. The species has great ability to persist even when its habitat is drained, and it often advances from ditches along railroads up the banks of the fills to high ground where it seems to thrive better than in a wet habitat. The habitat and the vigor of the plants greatly change the character of the leaves. Therefore, I believe it is useless to try to name all of the many forms.

Rhizomatous, functionally dioecious perennial, aquatic or amphibious or terrestrial, the terrestrial forms erect or ascending, to 1(-2) m, with hairy, typically lance-acuminate lvs, the more strongly aquatic forms with floating branches (and often stolons) and lvs, the lvs then glabrous, typically elliptic and obtuse or rounded; ocreae with or without a bristly fringe, in aerial forms often with a flared collar; racemes stout, dense, mostly 2-15 נ1-2 cm, usually borne singly or in pairs at the tips of major branches; tep 5, pink or red, bluntly rounded above, united below, 4-5 mm at anthesis, to 7 mm in fr, becoming veiny and enclosing the achene, this dark, shiny, doubly convex, 2.5-3 mm; 2n=66, 96, 98. Widespread in the N. Hemisphere, and in S. Afr. Our members of the species may be organized into 2 copiously intergrading ecotypic vars. The aquatic-adapted extreme, var. stipulaceum N. Coleman, flowers only when in water; its infls are to 4 cm, and the lvs are typically glabrous, floating, and elliptic. (P. natans; P. hartwrightii) The terrestrial-adapted extreme, var. emersum Michx., grows on land or is strongly emergent from shallow water, and does not produce floating leaves or shoots; its infls are 4-15 cm, the lvs are hairy and acuminate, and the peduncles are glandular-hairy. (P. coccineum; P. muhlenbergii). Var. amphibium is strictly Eurasian. (Persicaria a.)